Moths (and other insects) will circle bright objects, and thus appear to be attracted to light. The favored hypothesis advanced to explain this behavior is that moths and other night insects use a technique of celestial navigation called transverse orientation. By maintaining a constant angular relationship to a bright celestial light, such as the Moon, they can fly in a straight line. Celestial objects are so far away, that even after traveling great distances, the change in angle between the moth and the light source is negligible; further, the moon will always be in the upper part of the visual field or on the horizon. Human light sources have not existed for long enough to affect the evolution of moth navigation systems. When a moth encounters a much closer artificial light and uses it for navigation, the angle changes noticeably after only a short distance, in addition to often being below the horizon. The moth instinctively attempts to correct by turning toward the light, causing airborne moths to come plummeting downwards, and - at close range - which results in a spiral flight path that gets closer and closer to the light source.